Ed Gorman and others have recently discussed the "don'ts" in attempting a PI novel . The list is so extensive, I have almost always given it a pass. My one foray into it dealt with a retired PI so I could cheat. Having read hundreds of PI novels still doesn't make me an expert on avoiding cliches or employing tropes effectively.
I can more easily enter the arena of suspense where the requirements are less daunting. The thought of trying to pull off a SF novel or SF story is even more challenging. How long would it take to learn the vocabulary alone?
Do you stay away from attempting certain sorts of stories because of the pitfalls in trying to get it right? What is the hardest kind of story for you? Which subgenre is most butchered by amateurs?